The present disclosure relates to thermally actuated flow-control valves. More particularly, the present disclosure relates to valves including wax-filled actuators employed to control the flow of coolant to heat producing components in computing systems.
The use of wax-filled actuators or wax motors is well known. Wax motors have been employed to regulate the flow of fluids in a wide range of applications. Wax-filled actuators are utilized to prevent overheating in automotive systems and to regulate the flow of hot water in water heating systems for example. Such actuators are designed to open or close in response to a predetermined change in temperature. Wax-filled actuators are reliable temperature sensitive actuators that require no external energy, such as electricity or actuation force, such as a cable or lever.
In many temperature sensitive environments, it is desirable to stop or restrict flow of fluid to designated fluid passages when the fluid is cool and the wax actuator is closed. As the fluid warms up, the wax actuator begins to open, and permits fluid to flow. As the temperature of the fluid increases, the wax actuator progressively reaches its fully open, or fully “stroked” position, when the fluid reaches a predetermined operating temperature. The wax actuator fluctuates between the nominal opening position and the fully stroked position as the environmental temperature fluctuates.
The wax actuator conventionally comprises a rigid wax-filled cup, a guide and a piston received within the guide. The wax transitions between a solid and a liquid state over a predetermined temperature range, and typically expands in volume as the wax becomes a liquid. The guide is fixed to the cup and retains a flexible diaphragm to contain the wax in the cup. The guide defines an axial passage for a piston, which reciprocates in the axial passage according to pressure from the wax beneath the diaphragm. Thus, the axial length of the actuator changes according to the temperature of the wax, which is responsive to the temperature of the surrounding fluid.
The wax-filled actuator is typically positioned in a housing or aperture, with the piston arranged to deliver the force of the expanding wax to a valve member or to move the actuator body (the cup/guide) which may act as, or include a valve member. A return spring is also positioned to return the piston to its retracted/cold position when the temperature of the fluid falls and the wax returns to its smaller volume. The return spring is selected to overcome the friction of the piston in the axial passage and any linkage or valve associated with the actuator, to ensure reliable return to the closed or cold position.
The resulting valve assembly can be bulky, as the housing or aperture is sized to contain both the return spring and the wax-filled actuator. Generally speaking, there is demand for temperature actuated flow control valves that are compact and require as little volume as possible.
Fluid flow through a valve can be disrupted by turbulence caused by abrupt transitions of flow direction. Such abrupt transitions are typically associated with rapid changes of direction, such as when a fluid flows around a sharp corner. Compact fluid flow control valves can be prone to inefficient, turbulent flow because the smaller size of the fluid flow openings causes an increase in the rate of flow.
The need to position the actuator and return spring inside a housing or aperture complicates manufacture and/or assembly of the temperature sensitive fluid flow control valves.
Consequently there exists a need for a simple, compact and hydrodynamically improved thermally actuated flow-control valve.